Purification of internal combustion engine exhaust gas

ABSTRACT

Thermal reactor for mitigating or eliminating pollutants in automotive exhaust gas comprising an inner reaction chamber, an outer sleeve enclosing the reaction chamber, means for supplying cool air to the annular space thus formed between the reaction chamber and the sleeve, the chamber wall being formed with longitudinal slots (parallel to the chamber&#39;&#39;s axis) which are inclined relative to their respective radii from the center of the chamber so that air enters the chamber from the annulus and some circulates generally around the interior wall of the chamber thereby to protect it from high interior temperatures. Exhaust gas is passed to one end of the chamber from exhaust conduit(s) which are inclined in the same sense as the longitudinal slots and at roughly the same angle so that vortex circulation of exhaust gas and air is promoted in the chamber. The exhaust gas/air mixture reacts in the chamber, and purified gas passes out of the chamber at the centre of the opposite end.

United States Patent [191 Camarasa et a1.

[ Jan. 29, 1974 PURIFICATIONOF INTERNAL COMBUSTION ENGINE EXHAUST GASInventors: Mario Camarasa, Ostia Lido Rome, Italy; Bernhard Josef Kraus,Linden, NJ.

Esso Research Engineering Company, Linden, NJ.

Filed: June 12, 1972 Appl. No.: 262,132

Assignee:

US. Cl 60/290, 23/277 C, 60/282, 60/298, 60/305, 60/306 Int. Cl. F02!)75/10, FOln 3/10 Field of Search..... 60/298, 289, 290, 304, 305,60/306, 307, 323, 282, 317, 900; 23/277 C References Cited UNITED STATESPATENTS 5/1958 Kollgaard 60/310 5/1971 Brimer 60/282 12/1971Grainger.... 60/298 1/1972 I-Iaddad 60/323 4/1972 Evans 23/277 C FOREIGNPATENTS OR APPLICATIONS 7/1934 Great Britain ..60/298 PrimaryExaminer-Douglas Hart Attorney, Agent, or Firm-Leon Chasan et al.

[5 7] ABSTRACT Thermal reactor for mitigating or eliminating pollutantsin automotive exhaust gas comprising an inner reaction chamber, an outersleeve enclosing the reaction chamber, means for supplying cool air tothe annular space thus formed between the reaction chamber and thesleeve, the chamber wall being formed with longitudinal slots (parallelto the chambers axis) which are inclined relative to their respectiveradii from the center of the chamber so that air enters the chamber fromthe annulus and some circulates generally around the interior wall ofthe chamber thereby to protect it from high interior temperatures.Exhaust gas is passed to one end of the chamber from exhaust conduit(s)which are inclined in the same sense as the longitudinal slots and atroughly the same angle so that vortex circulation of exhaust gas and airis promoted in the chamber. The exhaust gas/air mixture reacts in thechamber, and purified gas passes out of the chamber at the centre of theopposite end.

13 Claims, 7 Drawing Figures TATENTED JAH 2 9 I874 sum 2 or 2PURIFICATION OF INTERNAL COMBUSTION ENGINE EXHAUST GAS The presentinvention relates to apparatus for purifying the exhaust gas from aninternal combustion engine, and more particularly, relates to acatalyst-free apparatus of the thermal reactor type in which suchexhaust gases are purified by reducing their content of unburned andpartially burned hydrocarbons (herein abbreviated to "HC), and carbonmonoxide.

Thermal reactors are already known, and are usually located in theexhaust system downstream of the exhaust manifold and upstream of thesilencer or muffler.

It is known in the art that the thermal reactors which have so far beenused for purifying the exhaust gases of motor vehicles are subject tothe action of high temperatures 700 C) which develop inside them duringthe reaction between combustible moieties in the exhaust gas and oxygen,causing serious wear and damage to the materials of which they are made,unless adequate protective measures are adopted, such as, for instance,

the injection of large amounts of excess air. .The presheat stresseswithout appreciable damage, or b) by adopting a system of the typealready known in the combustion chambers of gas turbines, viz. that ofkeeping the reacting gaseous mixture away from the surfaces of thereactor, with the aid of a thin film of air which acts as a screenforthe metal surfaces of the reactor, preventing them from becomingoverheated and avoiding the occurrence of injurious surface reactions.

Nevertheless, neither of the solutions examined has furnishedsatisfactory results. Indeed, the new materials proposed according to(a) have not always been found suitable, and in any case too costly,while on the other hand the heat reactors with walls protected by a filmof air according to proposal (b) have been carried out in structuresthat are generally very complicated, consisting of a number of parts,some of which (e.g., vanes or deflectors) always end by being damagedthrough the action of high temperatures, after a normal period ofoperation. I V

This latter point has necessitated the use of special materials for theconstruction of vanes and deflectors and this, in addition tothesomewhat large dimensions of the whole resulting reactor, makes its costrelatively unacceptable.

The present invention comprises apparatus for purifying the exhaust gasfrom the cylinder(s) of an internal combustion engine comprising areactor hollow, generally cylindrical form, a casing member surroundingthe reactor and fixedly spaced therefrom to provide an annular spacebetween the reactor and the casing member, at least one conduitextending through the said annular space and terminating at one end ofan exhaust gas entrance aperture of the reactor, and being adapted atits other end for conducting exhaust gas away from the engine, the gasconduit(s) being inclined, at the confluence with the reactor, at anangle of less than 90 with a radius from the centre of the reactorwhereby at least some exhaust gas entering the reactor from conduit(s),during operation, is caused to flow substantially tangentially withrespect to, or substantially parallel with, the inside wall of thereaction chamber at least one pipe communicating with the annular spacefor the supply of air to the annular space, a plurality of apertures inthe wall of the reactor for permitting cooling air to pass from theannular space into the reactor, the walls of each of said aperturesbeing inclined, relative to respective radii from the centre of thereactor, at an angle of less than 90 and in the same sense as the saidgas conduit(s) whereby to cause at least some air passing into thereactor from said apertures to flowgenerally tangentially relative to,or generally parallel to, the inside wall of the reactor, an exhaustconduit extending at least between a gas escape orifice defined in thewall of the reactor, and an adjacent discharge orifice in the wall ofthe casing member.

The actual angle of inclination of the walls of the apertures in thereactor can vary over wide limits, but preferred angles are in the rangeof from 30 to 75 and within this range, the apparatus of the inventionprovides satisfactory elimination of CO and HCs. The most preferredangle is about 60, this being a compromise between larger angles whichstrongly promote air flow around the internal wall of the reactor, andthe smaller angles which are easier to form in thin sheet metal. Themetal may be' sheet steel having a thickness in the range of 1.0 to 3.5mms., preferably 1.5 to 2.0 mms. thick.

ln order to maintain the temperatures in the reactor, during operation,adequately high for the combustion of CO and HC, it is preferred thatthe axial length of the reactor should be substantially equal to itseffective diameter (the effective diameter is the quotient of four timesthe cross-section area divided by the periphery). A preferred form ofthe reactor and the casing member is cylindrical.

The gas escape orifice is preferably defined by a wall at one axial endof the reactor, the other axial end being closed off, and the or eachentrance aperture for the exhaust gas is located adjacent to theclosed-off end of the reactor.

The inclined air apertures in the reactor walls each may be in the formof circumferentially spaced elongated slots which extend parallel to theaxis of the reactor over substantially the whole length of the reactorwall: those slots which extend towards the exhaust gas conduitspreferably do not extend completely up to the conduits.

The apparatus may further comprise an air off-take tube connected to thecasing member and communicating with the annular space, the off-taketube serving to conduct out of the annular space any air which does notpass into the reactor, the air supply pipe being connected for deliveryof air to the annular space in a generally circumferential directionaway from the air takeoff tube, the air off-take tube being so arrangedas to receive air from the annular space from a generallycircumferential direction away from the air cooling pipe. By thisarrangement of the air-supply and air off-take pipes, the possibilitythat air will pass directly from the supply to the off-take pipe is moreor less eliminated. The air off-take pipe and the air supply pipe arepreferably near to, or at, opposite ends of the reactor in order todecrease further the possibity of short-circuiting of air from thesupply pipe to the off-take pipe.

The off-take pipe may be connected to a distributor having airdistributing means for distributing air from the off-take pipe into aregion contiguous with the said other end of the exhaust gas conduit formixing air with exhaust gas in said region. It is preferred that the airthus distributed is directed towards the exhaust valves and ports of theengine to cool the valves and ports, and to causing mixing of air withthe exhaust gas when the exhaust gas is at its highest accessibletemperature.

Air which passes into the off-take pipe from the annulus will berelatively warm, and means may be provided for reducing the temperatureof the air in the offtake pipe to maintain a maximum air flowtherethrough.

It is advantageous to ensure, as far as possible, that heat losses fromthe reactor and casing member are minimised, and to this end, the airsupply pipe and the air off-take pipe may each be provided with aflangejoint having a gasket seal therein, the seals serving to mitigateheat conduction across the flange-joints. Thus, a jacket of relativelycool air is maintained in the annular space around the reactor, whilesome of the air passes through the inclined apertures into the reactorand, due to the tangential or vortex flow of gases therein, at leastsome of the air which passes into the reactor forms and replenishes athin film of relatively cool air or air-gas mixture which protects thereactor wall from the potentially damaging effects of the hightemperature burning gases enclosed by the thin film. Air which passesinto the reactor to mix with the high temperature exhaust gas inwardlyof the thin cool film is available as a source of oxygen for reactionwith potentially pollutant combustible materials in the exhaust gas, thevolume of the reactor being so chosen, according to principles which areknown in the art, to provide an adequate residence time for a requireddegree of combustion of said pollutant materials. During operation, thegases in the reactor should attain temperatures of 700 C or more, andpreferably at least 800 C, to ensure oxidation of most of thehydrocarbons and hydrocarbon products and 90 percent or more of thecarbon monoxide in the exhaust gas, while the'temperature of the reactorwall is always at least 200 C to 300 C lower than the reacting gastemperature e.g., the wall temperature may be 400 to 500 C (or lower).

It has been found that satisfactory operation of the apparatus of theinvention occurs even under conditions arising from defective ignitionin the engine, the use of an over-rich fuel-air mixture, or otherdefects in the engine.

The reactor may be relatively small, and most European automobiles wouldhave sufficient space in the engine compartment for receiving thereactor and its surrounding casing member.

The apparatus preferably further comprises means for supplying air,which means comprises an air pump or air fan driven directly from theengine or indirectly from an electrical power source, and ductingoperatively connected to the pump or fan, to the air supply pipe and tothe air distributor, there being means for regulating the absoluteamounts, and the relative proportions, of air passing to the air supplypipe and to the distributor. In one type of apparatus of the invention,there may be provided means responsive to the reactor temperature toshut off the supply of air to the annular space until the reactorattains a predetermined minimum temperature: in this way the reactor mayattain its normal operating temperature more rapidly. Such a temperatureresponsive means may comprise a bimetallic strip at the reactor end ofthe air supply pipe which acts on a throttle in the air supply pipeeither directly by mechanical linkage, or indirectly by acting as partof an electrical relay.

The apparatus of the invention may further comprise a valve operativelyconnected on one side to the air supply means and which valve is biassedtowards a closed position in which the passage of air therethrough isprevented, a conduit operatively connected at one end to the other sideof the valve and which is connectable, at its other end, to an intakemanifold of the engine, and means responsive to a selected depression ofpressure in a tube wich is connectable to the intake manifold forcausing movement of the valve away from its closed position, therebypermitting the passage of air from the air supply means to the saidconduit for passage into the intake manifold. This arrangement asdescribed prevents the intake manifold pressure from falling so lowduring certain engineoperating conditions particularly deceleration athigh speeds) that overenrichment of the fuel-air charge drawn into thecylinders of the engine is mitigated, at least to some extent, therebymitigating the amount of unburned and partially burned fuel which leavesthe engine in the exhaust gas.

The apparatus preferably comprises a plurality of exhaust gas conduits(e.g., one for each cylinder), the conduits all being disposed in orapproximately in, the same plane, and which plane is perpendicular tothe axis of the reactor.

The invention further includes the combination of a carburrettedinternal combustion engine having an intake manifold and at least oneexhaust valve or port, in operative connection with apparatus asdescribed hereinabove, with a respective exhaust gas conduit beingconnected to the engine for receiving exhaust gas from a respectiveexhaust valve.

Embodiments of the invention, given by way of nonlimitative exampleonly, will now be described with reference to the accompanying drawings,in which:

FIG. 1 is a schematic plan view ofa four-cylinder gasoline enginearrangement adapted in accordance with the invention;

FIG. 2 is a plan view of a horizontal section of part of the enginearrangement of FIG. 1;

FIG. 3 is a vertical cross-sectional elevation on line A-A of FIG. 2;

FIG. 4'is a vertical cross-sectional elevation on line BB of FIG. 2;

FIG. 5 is a schematic plan view of another engine arrangement adapted inaccordance with the invention;

FIG. 5a shows a cross-sectional view of the main components of a valveincorporated in the engine arrangement of FIG. 5, and FIG. 6 shows aschematic plan view of another engine arrangement adapted in accordancewith the invention. I

Referring first to FIG. 1, there is depicted an engine cylinder block100 having 4 cylinders 101a, 101b, 101C and 101d, and one side of theblock 101, an inlet manifold 102 having a carburettor 103 mountedthereon, and respective fuel-air mixture inlet pipes connecting theinlet manifold 102 to each cylinder 101.

On the opposite side of the block 100 from the inlet manifold 102, hotexhaust gases escape from each cylinder 101 through a respective curvedpipe 8, the pipes 8 heading to an exhaust gas thermal reactor 104whencefrom exhaust gas is passed to atmosphere via an exhaust pipe 105and a silencer or muffler 106.

With reference now to FIGS. 2, 3 and '4 of the drawings, there will beseen the reaction chamber of the thermal reactor 103 in the form of ahollow truncated cylinder 1 surrounded by an air gap 2 outwardly definedby a casing member wall 3 and communicating at 4 with a source of supplyof cooling air, delivered by a pump (not shown) of low output (e.g.,maximum delivery pressure 1.3 atmospheres). Through the wall 5 of thereactor chamber, longitudinal slit apertures 6 are formed which areequally apart in a circumferential sense and parallel to the axis of thereactor, extending throughout the entire length of the said reactionchamber 1, but without reaching the edges (a) and (b) (see in particularFIGS. 3 and 4), with the exception of some strips of the lateral surface(see FIG. 4), opposite I (andany secondary air) into the reactionchamber 1 at an angle, relative to a radius drawn to respective pipes 8,of less than 90 so that exhaust gas rotates in a vortex in the chambergenerally parallel to or tangential to the wall 5 of the chamber 1.

As will be noted only in FIGS. 3 and 4, the external casing 3 and theinternal casing 5 on each side of the air gap 2 are connected rigidlyopposite the outlet aperture 9 by means of fixing bolts 10.

It should be noted that the sides of the slits 6 are inclined inrelation to the corresponding radii so as to form with them an anglealpha 60. This, together with the formation of a tangentialflow of theexhaust gas (with any admixed secondary air), makes it possible to carryout one of the primary characteristics of the invention, viz, theformation inside the reaction chamber, throughout the entire inner wallof the casing 5, of a thin annular layer of air coming from 4 throughthe gap 2 and the slits 6. The said layer, which adheres closely to thesaid casing 5 is constantly being renewed and thus protects the actualcasing from the risk of excessive heating. As stated, the temperature ofthe said casing does not exceed 500 C, while inside the reaction chamberand its protective layer of air, the temperature is about 700 C.

The arrangement of the intake apertures 7 for the mixture of exhaust gas(and any secondary air) causes the formation of tangentialflow currentsinside the resupply pipe 4 directs air in one sense aroundthe annulus 2while the air off-take pipe has its off-take aperture oppositely facingwith respect to the air-supply pipe 4 to ensure that air travels aroundthe annulus before it is removed. Moreover, although not shown in FlG.5, the air supply pipe4 is at or near the axial end of the reactor 104so that cool air is provided at potentially the hottest end of thereactor, namely the end to which the pipes 8 are connected, and the airoff-take pipe has its off-take aperture at or near the opposite end ofthe reactor 104. By these relative'arrangements of the positions of airsupply to, and air removal from, the annulus, it is ensured as far aspossible that the possibility of air passing directly from the supplypipe 4 to the offtake pipe 13 is at most very small.

The air which passes into the air off-take 13 is mixed with a mainsecondary air supply at a Teeejunction, the main secondary air beingconveyed in a pipe 15 which receives air at one end from a main air line16 and discharges the main secondary air together with air from theoff-take line 13, through perforations (not shown) into a distributor17.- The distributor 17 is provided with nozzles 18 which pass air intothe region of connection of the exhaust conducting pipes 8 with theengine block, and more preferably, pass the airover the exhaust valve orport (not shown) of the engine. Thus, the exhaust valve or port isbeneficially cooled to some extent, while the hot exhaust gases,immediately on discharge from the cylinders, are mixed with the air andsome oxidation of unburned and incompletely burned fuel products cantake place as the exhaust gases pass via the pipes 8 into the reactionchamber 1 of the reactor 104.

restricting orifices with adjustable screws therein for regulating thecross-sectional areas of the orifices. Such valves and'restrictingorifices are well known to those skilled in the art, and theirparticular mode of construction does not form. an essential part of theI invention. For cheapness-and reliability, it is preferred actor, whichmakes it possible both to maintain a thin film of air adhering to thewall of the casing 5 and the immediate treatment of fresh portions ofthe incoming exhaust gas mixture as soon as it enters the reactor;combustion of potential pollutants is thus uniform, takes place morerapidly and therefore requires shorter reaction times: in consequence,reactors of reduced dimensions (compared with those of the prior art)may be employed.

Reference is now made to FIG. 5 of the drawings which again shows thecylinder block 100 and ancillaries of a carburetted internal combustionengine, and in which items common to FIGS. 1 to 4 are given the samereference numerals.

It will be seen that an air off-take pipe 13 is provided for removingfrom the air-containing annulus 2 any air which does not pass throughthe inclined slits 6 (not shown in FIG. 5) into the reaction chamber 1.The air to employ restricting orifices of a non-adjustable type, and itis preferred that 40-50 percent of the air from main air line 16 ispassed to the air inlet pipe shown in FlG. 5,7 the fan 20 is drivendirectly from the engine by a belt 21 and the speeds of the engine andfan 20 are preferably 1.0: 1.6 or thereabouts. Generally speaking, whenthe engine speed is equivalent to 50 km/hour, the flow rate of exhaustgas and secondary air passing through the reactor should be of the'orderof 600-700 litres/minute, and the cooling air should be supplied (e.g.,to inlet pipe 4) at a pressure of 1.3 atmospheres, or thereabouts. Theair supplied at pipe 4 should preferably always be at a pressureslightly in excess of the pressure in the reactor. The air dischargepipe 22 from the fan is connected to line 16 through a one-way checkvalve 23 so that pressure fluctations in line 16 and downstream thereofdo not substantially influence the pressure in the discharge pipe 22.

Between the fan 20 and the check valve 23 is ajunction tube 24 throughwhich air can pass to a so-called gulp-valve 25, the principal featuresof which are shown in FIG. 5a. Referring to FIGS. 5 and 5a together, itwill be seen that the valve 25 comprises air-tight enclosure 26 dividednear one end by a diaphragm 27 of flexible material, preferably anoil-resistant elastomer. Between the diaphragm 27 and the entranceaperture of tube 24 to the enclosure 26 is a plate 28 sealingly attachedat its periphery to the inside of the enclosure 26 and provided with anaperture 29 at or near to the centre of the plate 28. A valve member 30is attached at one end to the diaphragm 27 and has a tapered head endfor sealing against the aperture 29 when the resilient diaphragm 27 isnot deformed. The valve member 30 is subjected to a bias from a lightcompression spring 32 on the other side of the diaphragm 27 so that inits normal position, the valve member 30 closes the aperture 29. Betweenthe plate 28 and the diaphragm, the wall of the enclosure 26 has anaperture forming the entrance to an air-pressure compensating line 33which is connected at its other end to the inlet manifold 102 at aposition beneath the carburettor 103. A pressuresensing tube 34communicates pressure signals which are representative of pressurefluctuations in the inlet manifold 102 to that portion of the interiorof the enclosure 26 containing the spring 32.

During engine operation, any decrease in the pressure in the intakemanifold 102 is communicated to the gulp-valve via sensing-tube 34, andat a pre-selectable pressure, the difference in pressure across thediaphragm 27 will be sufficiently high to cause the diaphragm to deformagainst the bias of the spring 32 thereby causing the valve member 30 tomove from its closure position against the plate 28: the said pressuredifference then causes air to pass from the junction tube 24, throughthe aperture 29, and via the compensating line 33 into the intakemanifold, thereby tending to reducev the pressure depression therein,until the engine operating conditions or the total air flow through line33 are such that the pressure rises sufficiently to permit the spring 32to move the diaphragm 27 and the valve member 31 to a valve closingposition in which the aperture 29 is obturated. Excessive pressuredepressions occur when the throttle is partially or fully closed whilethe engine is operating at a relatively high speed (e.g., duringdeceleration) and such pressure depressions result in over-enrichment ofthe intake-manifold volume with fuel, most of which passes through theengine with very little complete combustion. By avoiding such pressuredepressions, the waste of fuel from this cause is considerably reduced,and the operating conditions in the reactor 104 are maintainedsubstantially constant (e.g., substantially constant temperatures in thereaction chamber 1).

Referring now to FIG. 6, the engine arrangement is more or less as inFIG. 5, and only the differences between the arrangements of FIGS. 5 and6 are hereinafter described. The main air line 16 supplies air to themain secondary air line '15 and the air inlet pipe 4 through separateair control means, which may be either adjustable valves, adjustableorifices, or fixed restricting orifices, 19a, 19b respectively. A checkvalve 36 in line 15 prevents pressure fluctuations at the valve portsbeing communicated into the main air line 16 (and corresponds, in itsfunction and effect, with the check valve 23 of FIG. 5).

The air inlet pipe 4 and the air off-take pipe 13 are connected torespective air conducting lines through flanged and bolted joints 37having gasket seals (not shown) therein. This type ofjointing permitseasier dismantling of the pipework connected to the reactor 104, andalso reduces heat loss by conduction from or into the reactor 104. Theair off-take pipe 13 is connected into the secondary air distributor 17via a pipe 13a, and a check valve 38 incorporated in pipe 13asubstantially prevents pressure fluctuations in the region of the engineexhaust valves or ports from being communicated via pipe 13 into thereactor 104.

The pipe 130 may be provided with fins 39 as illustrated, or other heatdissipating means, to cool air passing through pipes 13 and 13a so thata substantially constant mass flow of air passes into the distributor 17from off-take pipe: the provision of fins or other heat dissipatingmeans is an optional feature depending on the arrangement andcharacteristics of the engine, and the amount of ventilation of theengine compartment.

A further optional feature is the provision of means responsive to thereactor temperature to cut off the flow of air from the air inlet pipeso that the air in the annulus 2 insulates the reactor 1, and heatdissopation from the reactor by a current of air in the annulus 2 iseliminated, thereby decreasing the warm-up time of the reactor. Suchmeans are not shown, but they may take the form of a butterfly throttlevalve in line 4 which is actuated by a temperature dependent signal froman electrical transducer in, or on, the exhaust pipe 105 or a bimetallicelement located close to the reactor 104 which actuates a mechanicalthrottling device in the air line 4.

There are now given below, merely by way of illustration, the results ofsome tests that have been carried out by using a reactor according tothe invention in a motor vehicle subjected to a standardized workingcycle. The

test procedure adopted is the European Cycles in which the engine issubjected four times to an identical cycle passing from starting at lowspeed to a phase at 15 km per hour, then idling for a longer phase at 30km/hour, again at slow speed, and then a longer phase at 50 km per hourfollowed by a brief phase at 35 km per hour to return to idling and therepetition of the cycle. The time taken for the entire test is 20minutes; the external temperature is 2030 C. With a Fiat vehicle of typeS, when the reactor of the invention is not used, results were obtainedas given in the last line of the following table I, in whose first twolines are given the values of the percentages of CO and HC (totalhydrocarbons) allowed by current international legislation.

TABLE I Test cycles with engine operating according to Europeanprocedure (gl2 cycles) CO Cold test cycles according to Europeanprocedure (g/test) emission are obtained.

TABLE ll Cold Tests, gltest Hot tests g/Z cycles CO HC CO HC 40.00 1.013.5 0.22

This shows thebenefits arising from use of the reactor system accordingto the invention (reduction in the percentage of CO by 75 percent and BCby 80 percent).

It should be noted that by further modification of the carburettor-it ispossible further to reduce these figures, although at the cost of aslight increase in fuel consumption. (6-8 percent).

For instance, it has been noted in experiments that have been carriedout that by varying carburation and above all the quantitative ratiobetween secondary air and exhaust gas to keep the temperature in thereaction chamber above 700 C and to raise the content of oxygen in thedischarge gas to 1.5 percent, the following figures are found in the twotypes of cycles mentioned: CO 23.9, l-lC 0.9; CO 5.3; HC 0.13. thusobtaining greater purification and attaining the values: CO 15.0, HC0.35; CO 4.1, HC 0.06. when effecting a delay of about 10 percent inadvance at slow speed confined to the first cycle, i.e., when theengine, bieng cold, tends to produce higher percentages of C0 and HC inthe exhaust gas.

The present invention has been described with particular reference toits specific embodiments but it is intended that variationsandmodifications may in practice be made without departing from-theinvention as defined in the claims.

We claim:

1. Apparatus for purifying the exhaust gas from a cylinder of aninternal combustion engine comprising a reactor of hollow, generallycylindrical form, a casing member surrounding the reactor and fixedlyspaced therefrornto provide an annular space between the reactor and thecasing member, at least one conduit extending through the said annularspace and terminating at one end in an exhaust gas-entrnace aperture ofthe reactor, and being adapted at its other end for conducting exhaustgas away from the engine, the gas conduit being inclined, at theconfluence with the reactor, at an angle of less than 90 with a radiusfrom the centre of the reactor whereby at least some exhaust gasentering the reactor from the conduit, during operation, is caused toflow substantially tangentially with respect to, or substantiallyparallel with, the inside wall of the reaction chamber, at least onepipe communicating with the annular space for the supply of air to theannular space, a plurality of apertures in the wall of the reactor forpermitting cooling air to pass from the annular space into the reactor,the walls of each of said apertures being inclined, relative torespective radii from the centre of the reactor, at an angle of lessthan 90 and in the same sense as the said conduit whereby to cause atleast some air passing into the reactor from said apertures to flowgenerally tangentially relative to, or generally parallel to, the insidewall of the reactor, an exhaust conduit extendingat least between a gasescape orifice defined in the wall of the reactor, and an adjacentdischarge orifice in the wall of the casing member.

2. Apparatus according to claim 1 in which the said angle of inclinationof the walls of the apertures is from 30 to 3. Apparatus according toclaim 1 in which the axial length of the reactor is substantially equalto its effective diameter.

4. Apparatus according to claim 1 in which the gas escape orifice isdefined by a wall at one axial end of the reactor being closed off, andthe entrance aperture for the exhaust gas being adjacent the closed offend of the reactor.

5. Apparatus according to claim 1 in which the said apertures in thereactor walls are each in the form of circumferentially spaced elongatedslots which extend parallel to the axis of the reactor oversubstantially the whole length of the reactor wall.

6. Apparatus according to claim 1 in which there is provided an airoff-take tube communicating with the annular space for the passage ofair which does not pass through the apertures in the reactor, the airsupply pipe being connected for delivery of air to the annular space ina generally circumferential direction away from the air off-take pipe,and the off-take pipe being arranged to receive air from the annularspace from a generally circumferential direction away from the aircooling pipe.

7. Apparatus according to claim 6 in which the air off-take tube and theair supply pipe are substantially adjacent opposite ends of the reactor.

8. Apparatus according to claim 7 in which the air take-off tube isconnected to a distributor having air distributing means fordistributing air from said offtake tube into a region contiguous withthe said other end of the exhaust gas conduit for mixing air withexhaust gas in said region.

9. Apparatus according to claim 8 comprising means for cooling theoff-take tube for reducing the temperature of any air therein.

10. Apparatus according to claim 9 in which the air supply pipe isconnected to an air supply conduit by means of a flange-joint having agasket seal therein, and the air off-take tube is connected to saiddistributor by means comprising a flange-joint having a gasket sealtherein whereby heat loss by conduction from the reactor and easingmember is substantially reduced.

11. Apparatus according to claim 8 further comprising means forsupplying air, said means comprising an air pump or fan, ductingoperatively connected to the pump or fan and to the air supply pipe andto the air distributor, and means for regulating the amount and relativeproportions of air passing to the air supply pipe and to thedistributor.

12. Apparatus according to claim 11 comprising a valve operativelyconnected on one side to the air supply means, said valve being biassedtowards a closed position in which the passage of air therethrough isprevented, a conduit operatively connected at one end to the intakemanifold.

13. Apparatus according to claim 1 comprising a plurality of exhaust gasconduits, the conduits all being disposed substantially in a commonplane, the said plane being substantially perpendicular to the axis ofthe reacton

1. Apparatus for purifying the exhaust gas from a cylinder of aninternal combustion engine comprising a reactor of hollow, generallycylindrical form, a casing member surrounding the reactor and fixedlyspaced therefrom to provide an annular space between the reactor and thecasing member, at least one conduit extending through the said annularspace and terminating at one end in an exhaust gas entrnace aperture ofthe reactor, and being adapted at its other end for conducting exhaustgas away from the engine, the gas conduit being inclined, at theconfluence with the reactor, at an angle of less than 90* with a radiusfrom the centre of the reactor whereby at least some exhaust gasentering the reactor from the conduit, during operation, is caused toflow substantially tangentially with respect to, or substantiallyparallel with, the inside wall of the reaction chamber, at least onepipe communicating with the annular space for the supply of air to theannular space, a plurality of apertures in the wall of the reactor forpermitting cooling air to pass from the annular space into the reactor,the walls of each of said apertures being inclined, relative torespective radii from the centre of the reactor, at an angle of lessthan 90* and in the same sense as the said conduit whereby to cause atleast some air passing into the reactor from said apertures to flowgenerally tangentially relative to, or generally parallel to, the insidewall of the reactor, an exhaust conduit extending at least between a gasescape orifice defined in the wall of the reactor, and an adjacentdischarge orifice in the wall of the casing member.
 2. Apparatusaccording to claim 1 in which the said angle of inclination of the wallsof the apertures is from 30* to 75*.
 3. Apparatus according to claim 1in which the axial length of the reactor is substantially equal to itseffective diameter.
 4. Apparatus according to claim 1 in which the gasescape orifice is defined by a wall at one axial end of the reactorbeing closed off, and the entrance aperture for the exhaust gas beingadjacent the closed off end of the reactor.
 5. Apparatus according toclaim 1 in which the said apertures in the reactor walls are each in theform of circumferentially spaced elongated slots which extend parallelto the axis of the reactor over substantially the whole length of thereactor wall.
 6. Apparatus according to claim 1 in which there isprovided an air off-take tube communicating with the annular space forthe passage of air which does not pass through the apertures in thereactor, the air supply pipe being connected for delivery of air to theannular space in a generally circumferential direction away from the airoff-take pipe, and the off-take pipe being arranged to receive air fromthe annular space from a generally circumferential direction away fromthe air cooling pipe.
 7. Apparatus according to claim 6 in which the airoff-take tube and the air supply pipe are substantially adjacentopposite ends of the reactor.
 8. Apparatus according to claim 7 in whichthe air take-off tube is connected to a distributor having airdistributing means for distributing air from said off-take tube into aregion contiguous with the said other end of the exhaust gas conduit formixing air with exhaust gas in said region.
 9. Apparatus according toclaim 8 comprising means for cooling the off-take tube for reducing thetemperature of any air therein.
 10. Apparatus according to claim 9 inwhich the air supply pipe is connected to an air supply conduit by meansof a flange-joint having a gasket seal therein, and the air off-taketube is connected to said distributor by means comprising a flange-jointhaving a gasket seal therein whereby heat loss by conduction from thereactor and casing member is substantially reduced.
 11. Apparatusaccording to claim 8 further comprising means for supplying air, saidmeans comprising an air pump or fan, ducting operatively connected tothe pump or fan and to the air supply pipe and to the air distributor,and means for regulating the amount and relative proportions of airpassing to the air supply pipe and to the distributor.
 12. Apparatusaccording to claim 11 comprising a valve operatively connected on oneside to the air supply means, said valve being biassed towards a closedposition in which the passage of air therethrough is prevented, aconduit operatively connected at one end to the other side of the valveand which is connectable, at its other end, to an intake manifold of theengine, and means responsive to a selected depression of pressure in atube which is connectable to the intake manifold for causing movement ofthe valve away from its closed position, thereby permitting the passageof air from the air supply means to the said conduit for passsage intothe intake manifold.
 13. Apparatus according to claim 1 comprising aplurality of exhaust gas conduits, the conduits all being disposedsubstantially in a common plane, the said plane being substantiallyperpendicular to the axis of the reactor.